21720617 has 2 divisors, whose sum is σ = 21720618. Its totient is φ = 21720616.

The previous prime is 21720613. The next prime is 21720631. The reversal of 21720617 is 71602712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17007376 + 4713241 = 4124^2 + 2171^2 .

It is a cyclic number.

It is not a de Polignac number, because 21720617 - 2² = 21720613 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21720613) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860308 + 10860309.

It is an arithmetic number, because the mean of its divisors is an integer number (10860309).

Almost surely, 2^21720617 is an apocalyptic number.

It is an amenable number.

21720617 is a deficient number, since it is larger than the sum of its proper divisors (1).

21720617 is an equidigital number, since it uses as much as digits as its factorization.

21720617 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1176, while the sum is 26.

The square root of 21720617 is about 4660.5382736332. The cubic root of 21720617 is about 279.0127519083.

The spelling of 21720617 in words is "twenty-one million, seven hundred twenty thousand, six hundred seventeen".